1. Field of the Invention
The present invention relates to electronically conducting cable or wire having a high surface area to reduce attenuation of high frequency signal transmissions due to the skin effect.
2. Description of the Related Art
The main properties of a cable are its inductance, capacitance, effective shunt conductance, and series resistance per unit length. Taken together, these properties include the signal transmission and loss properties when a length of cable is employed as part of a system. As signals are being transmitted through cables at higher and higher frequencies, loss or attenuation is becoming a big problem. The two main reasons for attenuation in cables are dielectric loss and skin effect. However, the effect of dielectric loss in cables is minimum and skin effect dominates the loss and attenuation in cables.
The skin effect is the tendency of an alternating electronic current (AC) to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. That is, the electric current tends to flow at the “skin” of the conductor. The skin effect causes the effective resistance of the conductor to increase with increasing frequency of the current. In fact, the skin depth is inversely proportional to the operating frequency.
FIG. 1 is a cross-sectional view of a typical round conductor cable 10. At frequencies below about 100 MHz, the electronic current flows throughout the cable with a fairly uniform distribution. In other words, there is no part of the wire cross-section that carries substantially more current than any other part of the wire cross-section. However, as the frequency increase above about 100 MHz, the flow of current begins to concentrate near the surface or “skin” of the wire. At much higher frequencies, the entire current will flow in a very narrow band or skin 12 on the conductor, such that only a small percentage of the total cross-sectional area of the cable 10 is effective for conducting high frequency current
One approach that attempts to deal with the skin effect is increasing the diameter of the conductor cable to provide a larger surface area over which the current can flow. However, this approach produces very large, bulky cables and makes inefficient use of the metal conductor. Another approach plates the conductor cable with gold or silver to modify the frequency response within the cable and lower the resistivity of the cable at higher frequencies.
Yet another approach has been to cut or shape a conductor cable to increase the amount of surface area. However, these types of increased surface area have still not led to the development of a conductor cable having the desired low resistivity at high frequencies. Therefore, there remains a need for a conductor cable that provides low resistivity under high frequency current.